8-2-20 Earth to birds: Take the next left
Every fall, the bar-tailed godwit takes to wing and flies nonstop from Alaska to New Zealand — a journey of 7,000-plus miles. Countless other birds head off too, bound for warmer spots before returning in the spring. How they do it without getting lost remains mysterious to this day. Scientists are convinced birds must be using some type of biologically based magnetic compass, but they have yet to figure out how such a system would work. Now the field is heating up, and the latest research is pointing away from one long-standing theory and bolstering some intriguing alternatives. Clues have been piling up for decades. Back in the 1960s, researchers discovered that European robins can somehow sense Earth's magnetic field. In the decades since, scientists learned that robins and a variety of other bird species use the field, which is created by movement of iron in Earth's core, as a navigational aid. The birds combine this guide with information deduced from the sun, the stars, and geographical landmarks to complete their voyages. But a vexing question that remains is what sort of biological receptor birds use to detect the magnetic field. "Key experiments by a group in Germany definitively showed that a magnetic sense exists. Now, more than 50 years later, we still don't really understand how it works," says neuroscientist David Keays of the Research Institute of Molecular Pathology in Vienna. Today, researchers are focusing on three possible ways that a magnetic sense could work. One idea involves a form of iron with magnetic properties, called magnetite, acting as a sort of compass within cells that rotates to align with the magnetic field. Another contender, known as the radical-pair mechanism, hinges on a chemical reaction in a bird's eye that is influenced by Earth's magnetic field. A third hypothesis suggests that as a bird moves through Earth's magnetic field, small currents are generated in the creature's inner ear. In all three of these scenarios, signals are produced and passed on to the bird's brain to be processed and translated into directions. Here's a look at each of them. 1. The magnetite idea has been studied the longest. Though it is biologically possible — certain kinds of swimming bacteria use the iron mineral to orient themselves — evidence in higher animals remains elusive, with scattered reports that are not always reproducible. 2. The weight of evidence gathered by scientists tilts toward another idea known as the radical-pair hypothesis, Hore says. Mouritsen also favors this idea, which is based on a protein in birds' eyes called cryptochrome. 3. Keays is testing a long-forgotten hypothesis, first proposed in 1882, that as a bird flies through Earth's magnetic field, tiny electric currents are generated in its ear. This would happen through electromagnetic induction, akin to how a magnet that moves through a coiled wire creates an electric current in the wire.
8-1-20 To save Appalachia’s endangered mussels, scientists hatched a bold plan
To save Appalachia’s endangered mussels, scientists hatched a bold plan. The emergency surgery took place in the back of a modified pickup truck in a McDonald’s parking lot in Pikeville, Ky. This scrappy plan to rescue a species of mussel on the edge of extinction made perfect sense: Meet somewhere between Indian Creek in Virginia, where the last known wild golden riffleshells lived, and Kentucky’s Center for Mollusk Conservation in Frankfort, where they would be saved. The strategy was a malacologist’s version of a Hail Mary pass. One scientist would gingerly pry open three golden riffleshells and remove their larvae to be nurtured in his lab. The other would return the three mussels to Indian Creek, and wait for the day he could introduce their grown offspring to the same habitat. If the plan didn’t produce enough offspring to sustain a new population, the mussels would probably vanish. Five years ago, Indian Creek was the only known remaining habitat for the golden riffleshell (Epioblasma florentina aureola). And like many other mussels, this bivalve’s future looked bleak. Biologists estimated that only about 100 remained in the wild. “They were the next species on the list for disappearing from the face of the Earth,” says biologist Tim Lane, who leads mussel recovery efforts at the Virginia Department of Wildlife Resources’ Aquatic Wildlife Conservation Center, near Marion. “We were literally watching the last of them.” Seeing a species vanish in real time is difficult, he says, and is in some ways worsened by the mussels’ near-invisibility beneath the surface. “They’re not charismatic like, say, the northern white rhino,” he says. When mussels go extinct, almost no one knows — or mourns them. An avid amateur photographer who takes pictures of mollusks, snails, fish and various other small critters in the wild, Lane spends much of his time floating facedown in Appalachian waterways, suspended over rocky riverbeds like a float in the Macy’s Thanksgiving Day Parade. He came up with the plan and carried out phase one: delicately prying the bivalves from the Indian Creek river-bed and laying them in a cooler filled with pebbles, dirt and river water for the 90-minute trip to Kentucky.